EFFECT OF THE METABOLIC PRODUCTS 217 



9. Explain the mutual action and the changes which 

 occur. 



10. What enzymes are responsible for each change? 

 Write out the chemical equations for each change, giving 

 enzyme concerned in each case. 



Was the theoretical amount of alcohol changed into 

 acetic acid? Give a reason for what really does happen. 



What phase of mutual relationship is illustrated? 



What is the classical example of this type of mutual 

 relationship? 



11. Give data and observations in full and draw conclu- 

 sions. Point out any practical applications. 



REFERENCES 



MARSHALL: Microbiology, pp. 182-183, 448-458. 

 LAFAR: Technical Mycology, Vol. I, pp. 297-307; Vol. II, Part 2, 

 pp. 473-481, 511-515. 



EXERCISE 33. TO DEMONSTRATE THE EFFECT OF 

 THE METABOLIC PRODUCTS OF BACT. LACTIS 

 ACIDI ON ITS ACTIVITIES 



Apparatus. Two sterile 200 c.c. flasks. 200 c.c. sweet 

 skim milk; azolitmin solution; apparatus for titration; 

 sterile dilution flasks; sterile Petri dishes; sterile 1 c.c. 

 pipettes; sterile 5 c.c. pipettes; sterile 10 c.c. pipettes; 

 ten to fifteen tubes of sterile litmus milk. 



Culture. Bad. lactis addi (twenty-four-hour culture). 



(At least two weeks should be allowed for the completion of 

 this experiment.) 



Method. 1. Place 100 c.c. skim milk, +10 to +15 

 (record acidity before adding azolitmin), in each flask and 

 sterilize by the Tyndall method. 



2. Mark the flasks A and B. 



3. Inoculate each flask with a loopful of a twenty-four- 

 hour milk culture of Bact. lactis acidi. Mix well with a 

 needle and plate dilutions 1-10, 1-100, 1 10,000 from flask 



